Lamp base



FIG. 1 is a perspective view of a lamp base showing my new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a left side view thereof; and,

FIG. 6 is a top plan view thereof.

The broken line showing of environmental structure is for illustrative purposes and does not form a part of the claimed design. 

The ornamental design for a lamp base, as shown and described. 